Levels and Curves

When it comes to color correction, Levels and Curves offer you the most control. Both commands allow you to make selective as well as global corrections by applying nonlinear adjustments. They are also both available as adjustment layers. Unlike the legacy  version of Brightness/Contrast, which applies linear transformations (adjusting the overall image in equal amounts), Levels and Curves allow you to adjust values in the middle of the tonal range without losing information at the ends. This nonlinear adjustment method allows you to preserve highlight and shadow detail as you improve your images. Of the two commands, Levels is easier to master, but Curves is more powerful. Keep in mind that everything you can do with Levels can also be done with Curves, but working with Curves requires more skill and effort. Curves is the tool to use for detailed tonal corrections, whereas Levels is best suited for quick global corrections, such as lightening the midtones or increasing overall image and contrast.